Process and device for constructing a synthetic image of the environment of an aircraft and presenting it on a screen of said aircraft

ABSTRACT

The device ( 1 ) comprises information sources ( 2 ) comprising information relating to the aircraft and to its environment, information processing means ( 3 ) able to construct a synthetic image of the environment of the aircraft on the basis of information emanating from the information sources ( 2 ) and display means ( 5 ) able to present, on at least one part of a display screen ( 7 ), a synthetic image. This image is constructed with the aid of a conical projection onto a plane of projection which is orthogonal to a line of aim which forms angles of lateral separation and angles of vertical separation with the course of the aircraft.

[0001] The present invention relates to a process and a device fordisplaying synthetic images on an aircraft, in particular a civiltransport airplane. More precisely, said process and said device areintended for constructing a synthetic image of the environment of theaircraft and for presenting it to at least one pilot of said aircraft.

[0002] It is known that the navigation and operation of aircraft, inparticular of civil transport airplanes, may give rise to considerablework loads for the crews and the air traffic control. In particular,certain flight phases or conditions may be apt to engender greater orlesser dispersion of the attention of pilots. The complex synthesis ofpiloting and navigation data and of the states of the aircraft's systemsmay then not take place in an optimal and complete manner. Theconstruction of false mental images of the actual situation of theaircraft in space, in particular as regards the vertical margins withrespect to the terrain, may be the cause of untimely or erroneousjudgements and behaviors.

[0003] Furthermore, during the use of flight management computers (forexample of “FMS” type: “Flight Management System”), difficulties mayappear in the programming and analysis of the flight plan confirmed bythe crew. Awareness of the trajectory piloted by the automaticfacilities in relation to the outside environment is not immediate. Theprogramming gives rise itself to a sizeable workload. It may also beerroneous, with awareness of the error coming later.

[0004] The two points mentioned above, namely, on the one hand, the lackof awareness of the vertical margins of the aircraft and, on the otherhand, the difficulties in dialogue and in programming the flightmanagement computers, may sometimes be the cause of accidents of theaircraft by contact with the terrain. These two points may becharacterized by an overall lack of situational awareness. Situationalawareness is a synthesis of mental models constantly updated bycognitive and physical activities. The performance of the automaticfacilities may aid the crew during a situation of risk, but rarelyincreases the situational awareness of the pilots. Moreover, improvementof the situational awareness generally demands a considerable mentaleffort. The civil aviation sector is therefore seeking simple andintuitive means for aiding pilots to instantaneously ascertain theposition of the aircraft in its environment, at the present instant andin the minutes to come.

[0005] A subject of the present invention is a process making itpossible to construct a synthetic image which, when it, is presented toa pilot of an aircraft, makes it possible to aid the latter to improvethe awareness that he has of the situation of the aircraft.

[0006] For this purpose, said process is noteworthy, according to theinvention, in that:

[0007] a) a first straight line passing through the location of theaircraft and forming a first angle of lateral separation α and a firstangle of vertical separation β with the course of the aircraft isdetermined;

[0008] b) a first point is determined, said point being situated on saidfirst straight line to the rear of the aircraft at a distance such thatthe vertical projection of this first point onto the horizontal planepassing through the location of the aircraft, is situated at apredetermined distance L1 from said location of the aircraft; a line ofaim passing through said first point and forming a second angle oflateral separation va and a second angle of vertical separation vb witha second straight line passing through said first point and parallel tosaid course of the aircraft is determined;

[0009] d) a plane of projection which is orthogonal to said line of aimis defined;

[0010] e) an image is constructed of at least a part of the environmentat least in front of the aircraft, with the aid of a conical projectiononto said plane of projection while taking account of said first pointas reference point of the projection;

[0011] f) said image is delimited laterally by two vertical straightlines respectively cutting the horizon line of the image at second andthird points which are such that, on the one hand, the angle between theline of aim and a third straight line passing through said first andsecond points corresponds to a predetermined angle and, on the otherhand, the angle between the line of aim and a fourth straight linepassing through said first and third points corresponds to apredetermined angle;

[0012] g) the scale of the image thus delimited is adapted so as tomatch the straight line segment which is formed by said second and thirdpoints and which defines the width of the image, to the width of adisplay screen on which one wishes to present said image, and this imageis delimited vertically as a function of the height of said displayscreen; and

[0013] h) the image thus constructed representing a synthetic image ispresented on said display screen.

[0014] Thus, by virtue of the invention, said process makes it possibleto construct a synthetic image in three dimensions for displaying theposition (or the location) of the aircraft, as well as the environmentin which this aircraft is deploying. This synthetic image is constructedaccording to a viewpoint outside the aircraft. The display (or thepresentation) of this image on the display screen, which is for examplesituated in the piloting station of the aircraft, makes it possible toimprove the awareness that the pilot has of the actual situation of theaircraft.

[0015] Advantageously:

[0016] said first angle of lateral separation α lies between 6° and 15°;and/or

[0017] said first angle of vertical separation β lies between 3° and10°; and/or

[0018] said predetermined distance L1 lies between 3 and 20 kilometers;and/or

[0019] said second angle of lateral separation va is less than or equalto said first angle of lateral separation α; and/or

[0020] said second angle of vertical separation vb is less than or equalto said first angle of vertical separation β.

[0021] Furthermore, in a particular embodiment, said display screen isfurnished with a heading scale and said angles between the line of aimand said third and fourth straight lines are such that the angulardiscrepancy on the heading scale between said second and third pointslies between 40° and 140°.

[0022] Additionally, advantageously, in step g), the image is delimitedvertically in such a way that the horizon line of said image is situatedin the upper third of said display screen.

[0023] Furthermore, advantageously, in step e), only an image of theenvironment which is situated up to a predetermined distance in front ofthe aircraft is constructed.

[0024] In a preferred embodiment of the invention, the image constructedin step e) comprises at least the following elements:

[0025] a first symbol representing the aircraft and indicating itslocation;

[0026] a representation illustrating the terrain;

[0027] a vertical reference stroke between said symbol of the aircraftand its vertical projection on said terrain; and

[0028] a first plot representing the future trajectory of the aircraft.

[0029] Thus, the image constructed makes it possible to improve thepilot's awareness of the overall situation of the aircraft, inparticular as regards the outside environment, and its future trajectorywith respect to this outside environment.

[0030] Furthermore, advantageously, the image constructed in step e)moreover comprises:

[0031] a second plot representing the vertical projection onto saidterrain of the future trajectory of the aircraft; and/or

[0032] a plurality of vertical strokes between points situated on saidfirst plot representing the future trajectory of the aircraft and thecorresponding vertical projections. Preferably, at least one of saidvertical strokes comprises a safety altitude indication; and/or

[0033] a heading scale represented above the horizon line; and/or

[0034] a flight plan; and/or

[0035] supplementary information, for example information about the airtraffic or the weather.

[0036] Additionally, advantageously, said vertical reference strokecomprises a scale and/or an indication of safety altitude.

[0037] Furthermore, advantageously, said first symbol representing theaircraft is representative of the attitudes of the aircraft in roll,pitch and yaw.

[0038] Additionally, advantageously, said representation illustratingthe terrain is colored as a function of the discrepancy between thealtitude of the aircraft and the altitude of said terrain.

[0039] Furthermore, advantageously, any risk of collision of theaircraft with the terrain is detected by calculating the distancebetween the future trajectory of the aircraft and said terrain, and afirst alarm indication is presented on said image when such a risk ofcollision is detected.

[0040] Moreover, advantageously, any risk of intersection of a flightplan of the aircraft with the terrain is detected by calculating thedistance between a trajectory corresponding to this flight plan of theaircraft and said terrain, and a second alarm indication is presented onsaid image when such a risk of intersection is detected.

[0041] In a particular embodiment, a rotation of the line of aim by apredetermined angle about the aircraft is carried out. This makes itpossible to be aware of the situation of the aircraft with respect tothe terrain situated behind it or to the sides, as specifiedhereinbelow.

[0042] The present invention also relates to a device for constructing asynthetic image of the environment of an aircraft and presenting it toat least one pilot of said aircraft.

[0043] According to the invention, said device of the type comprising:

[0044] information sources comprising information relating to theaircraft and to its environment;

[0045] information processing means able to construct a synthetic imageof the environment of the aircraft on the basis of information emanatingfrom said information sources; and

[0046] display means able to present, on at least one part of a displayscreen, said synthetic image, is noteworthy in that said informationprocessing means are formed in such a way as to implement the processspecified under claim 1.

[0047] Thus, said device according to the invention provides arepresentation which shows the terrain, the position of the aircraft andof its future trajectory, as well as possible alerts of risks ofcollision with the terrain and of crossing of safety altitudes, in theform of a three-dimensional image. This three-dimensional image isdirectly and intuitively accessible to the pilots, without particulareffort.

[0048] The device in accordance with the invention, which thereforemakes it possible to aid pilots to instantaneously ascertain theposition of the aircraft in its environment, at the present instant andin the minutes to come, consequently affords a valuable aid to theawareness of the situation of the aircraft in relation to the terrainand considerably increases flight comfort and safety.

[0049] The figures of the appended drawing will elucidate the manner inwhich the invention may be embodied. In these figures, identicalreferences designate similar elements.

[0050]FIG. 1 is the schematic diagram of a device in accordance with theinvention.

[0051] FIGS. 2 to 8 and 11 illustrate various depictions enabling theimplementation of the process in accordance with the invention to beproperly portrayed.

[0052]FIGS. 9 and 10 are two partially cutaway views which show twoimages constructed in accordance with the present invention, which arepresented on a display screen and which relate respectively to twodifferent situations.

[0053] The device 1 in accordance with the invention and representeddiagrammatically in FIG. 1 is intended for the construction of asynthetic image IM of the environment of an aircraft A, in particular ofa civil transport airplane, and for its presentation to at least onepilot of said aircraft A.

[0054] To do this, said device 1 which is carried on board the aircraftA is of the type comprising:

[0055] information sources 2 comprising, for example, sensors,computers, onboard systems, etc., which provide information relating tothe aircraft A and to its environment;

[0056] information processing means 3 connected by a link 4 to saidinformation sources 2 and able to construct a synthetic image IM of theenvironment of the aircraft A on the basis of information emanating fromsaid information sources 2; and

[0057] display means 5 connected by a link 6 to said informationprocessing means 3 and able to present, on at least one part of adisplay screen 7, said synthetic image IM.

[0058] According to the invention, said information processing means 3implement a process comprising the string of following steps consistingin:

[0059] a/ determining a straight line D2 passing through the location ofthe aircraft A and forming an angle of lateral separation a and an angleof vertical separation β with the course DR of the aircraft A (FIGS. 2and 3). The expression location of the aircraft A is understood to meanits spatial position and more precisely the spatial position of itscenter of gravity.

[0060] To do this, in a first variant, a straight line D1, situated in ahorizontal plane, forming an angle of lateral separation α with theinstantaneous course DR of the aircraft A and cutting this course at thecurrent location of the aircraft A is determined, as represented in FIG.2. Next, said straight line D2, which is situated in the same verticalplane as the straight line D1, which forms an angle of verticalseparation β with the straight line D1 and which cuts said straight lineD1 and also said course DR at the current location of the aircraft A isdetermined, as represented in FIG. 3. It will be noted that theinstantaneous course DR forms a generally non-zero angle with thelongitudinal axis AL of the aircraft A in FIGS. 2, 4 and 5.

[0061] In a second variant (not represented), a straight line D1A (notrepresented) forming an angle of vertical separation β with theinstantaneous course DR of the aircraft A is firstly determined, thensaid straight line D2 which exhibits an angle of lateral separation αwith this straight line D1A is formed;

[0062] b/ determining a point V which is situated on said straight lineD2 to the rear of the aircraft A at a distance such that the verticalprojection V1 of this point V onto the horizontal plane passing throughthe location of the aircraft A, is situated at a predetermined distanceL1 from said location of the aircraft A, as represented in FIGS. 3 and4;

[0063] c/ determining a line of aim LV (FIG. 6) passing through saidpoint V and forming an angle of lateral separation va and an angle ofvertical separation vb with a straight line D3 passing through saidpoint V and parallel to said course DR of the aircraft A.

[0064] To do this, in a first variant, a straight line D4 which passesthrough the point V, which is situated in a horizontal plane, and whichforms an angle of lateral separation va with the straight line D3 isdetermined, as represented in FIG. 5. Next, the line of aim LV, which issituated in the same vertical plane as the straight line D4, and whichforms an angle of vertical separation vb with the straight line D4 andwhich cuts the straight line D4 at the point V is determined, asrepresented in FIG. 6.

[0065] In a second variant (not represented), a straight line D4A (notrepresented) forming an angle of vertical separation vb with thestraight line D3 is firstly determined, then the straight line LV whichforms an angle of lateral separation va with the straight line D4A isdetermined;

[0066] d/ defining a plane of projection PP which is orthogonal to saidline of aim LV and which is situated at an arbitrary distance L2 fromsaid point V. Said line of aim LV cuts the plane of projection PP at apoint O (FIG. 7);

[0067] e/ constructing an image IM of at least a part of the environmentat least in front of the aircraft A, with the aid of a conicalprojection onto said plane of projection PP while taking account of saidpoint V as reference point of the projection, as will be seen in greaterdetail hereinbelow;

[0068] f/ laterally delimiting said image IM by two vertical straightlines 8 and 9 cutting, as represented in FIG. 7, respectively thehorizon line 10 of the image IM at points 11 and 12 which are such that,on the one hand, the angle θ1 between the line of aim LV and a straightline 13 passing through said points V, 11 corresponds to a predeterminedangle and, on the other hand, the angle θ2 between the line of aim LVand a straight line 14 passing through said points V, 12 corresponds toa predetermined angle;

[0069] g/ adapting the scale of the image IM thus delimited so as tomatch the straight line segment 15 which is formed by said points 11, 12and which defines the width of the image IM, to the width of the displayscreen 7 on which one wishes to present this image IM, and this image IMis delimited vertically as a function of the height of said displayscreen 7. Preferably, the vertical limitation of the image IM is suchthat the horizon line 10 of this image IM is situated substantially inthe upper third of the display screen 7; and

[0070] h/ transmitting the image IM thus constructed which represents asynthetic image to said display means 5 so that they present it on saiddisplay screen 7.

[0071] Thus, said information processing means 3 make it possible toconstruct a synthetic image IM in three dimensions so as to display theposition (or the location) of the aircraft A, together with theenvironment in which this aircraft A is deploying. This synthetic imageIM is constructed according to a viewpoint.(point V) outside theaircraft A. The display (or the presentation) of this image IM on thedisplay screen 7, which is for example situated in the piloting stationof the aircraft A, makes it possible to improve the awareness that thepilot has of the actual situation of the aircraft A. This display screen7 may be a specific screen or an existing screen already on the aircraftA, such as a standard navigation screen of “ND” (“Navigation Display”)type.

[0072] In a preferred embodiment of the invention:

[0073] the value of the angle α (step a) lies in an intervalsubstantially equal to [6°; 15°]. Preferably, the angle α issubstantially equal to 9° or 10°;

[0074] the value of the angle β (step a) lies in an intervalsubstantially equal to [3°; 10°]. Preferably, the angle β issubstantially equal to 5° or 6°;

[0075] the value of the distance L1 (step b) lies in an intervalsubstantially equal to [2 Nm; 10 Nm] (around [3.7 km; 18.5 km]), Nmbeing a nautical, mile, the international unit of distance measurementemployed in aeronautics and equal to 1852 meters. Preferably, thedistance L1 is substantially equal to 5 Nm (around 9.3 kilometers);

[0076] the value of the angle va (step c) preferably lies in an intervalsubstantially equal to [0; α]. When va=0, the line of aim LV is situatedin a vertical plane parallel to the course DR of the aircraft A. Whenva=α, the line of aim LV is such that the representation of the aircraftA is situated at the center of the image IM; and

[0077] the value of the angle vb (step c) preferably lies in an intervalsubstantially equal to [0; β].

[0078] It will be noted that the construction of the image IM has beenrepresented in FIGS. 2, 4 and 5 in the case where the point V issituated slightly to the right at the rear of the aircraft A. Withoutdeparting from the scope of the present invention, an image maynaturally also be constructed from a point V which is situated slightlyto the left at the rear of the aircraft A.

[0079] Additionally, the projection used in step e) is a standardconical projection. It is known that such a conical projection (orcentral projection) is by construction the representation closest to ourvisual perceptions. It makes it possible in particular to see a sphereas a circle. A conical projection of three-dimensional space is aprojective transformation which sends all the points of this space ontoone and the same plane of projection PP of this space. It requires thata reference point V (equivalent to the position of the eye of anobserver) and a plane of projection PP (Dürer's glass, the equivalent ofthe retina) [FIGS. 7 and 8] be given. The image μ of a point M underthis conical projection is defined as the intersection of the straightline VM (equivalent to the light ray coming from the point M reachingthe eye V) with the plane of projection PP. Unlike affine projections,the conical projection does not preserve the barycentet (hence theratios of lengths on a given straight line). It only preserves thealignment and the cross ratio. It will be noted moreover that the pointO (point of intersection of the straight line LV with the plane ofprojection PP) belongs to a straight line corresponding to therepresentation of the horizon line 10 in the plane of-projection PP.This line corresponds to the projection of points situated at infinity.According to this conical projection, two parallel straight lines inspace are represented as converging to one and the same point which issituated at infinity, and which is therefore represented on this horizonline 10.

[0080] The representation of FIG. 8 allows a proper portrayal of saidconical projection. In this FIG. 8 are represented:

[0081] the plane of projection PP which is orthogonal to the line of aimLV passing through the point V and cutting this plane of projection PPat the point O;

[0082] a plan P1 which is orthogonal to said plane of projection PP;

[0083] the course DR and the heading CAP of the aircraft A, which cutthe plane of projection PP respectively at points 17 and 18 whichtherefore illustrate the course DR and the heading CAP on the image IM;

[0084] a point 19 illustrating the position of the aircraft A andcorresponding to the point of the plane of projection PP that cuts thestraight line passing thorough the point V and the aircraft A;

[0085] a point Ω corresponding to the projection of the point V onto theplane P1; and

[0086] points M1 and M which are situated on said plane P1, the straightlines ΩM1, ΩM and VM cutting the plane of projection PP at points 01, μ1and μ respectively.

[0087] The conical projection makes it possible to obtain the followingequations in particular: $\left\{ \begin{matrix}{\frac{01\mu \quad 1}{M1M} = \frac{\Omega \quad 01}{\Omega \quad {M1}}} \\{\frac{\mu \quad \mu \quad 1}{V\quad \Omega} = {\frac{M\quad \mu \quad 1}{M\quad \Omega} = \frac{M101}{{M1}\quad \Omega}}}\end{matrix}\quad \right.$

[0088] In a particular embodiment of the invention, the pilot of theaircraft A has available a function that he can activate (for example bypressing a key (not represented)) to cause a rotation of the line of aimLV by a predetermined angle about the aircraft A, by increasing thevalue of the angle α by the value of this predetermined angle, so as tobe aware of the situation of the aircraft A with respect to the terrainwhich is situated behind the aircraft A (angle of 180°) or to the sides(angles of ±90°). Such a function is particularly advantageous in thephases of approach to an airport or of turning of the aircraft A. In avariant of this particular embodiment, the line of aim LV is rotated bya predetermined angle about the point V, without modifying the angle α.Thus, for a value of said predetermined angle equal to 180°, it ispossible to display an image of the terrain situated behind the aircraftA, said image not representing the aircraft.

[0089] Additionally, it is known that, on a navigation screen of “ND”type (“Navigation Display”) of an aircraft A, in the so-called “ARC” or“ROSE” modes, the display comprises a so-called “heading scale”graduation which corresponds to all or part of a graduation from 0 to360° centered on this aircraft A, the value 0 of this graduationcorresponding to North. For each angular value of the heading scale, itis possible to define a straight line passing through the center ofgravity of the aircraft A and forming an angle corresponding to thisangular value, with respect to the 0° direction of this heading scale.The representation of this straight line in the plane of projectionconverges (at infinity) to a point situated on the horizon line. It isthus possible to define a heading scale associated with the virtualimage constructed in the plane of projection: this heading scaleconsists of a set of points on the horizon line, this amounting tograduating the horizon line in angular values of the heading scale. Forreasons of homogeneity of display between such a “ND” screen and thevirtual image IM which is the subject of the present invention, in apreferred embodiment, when a “ND” screen is used as display screen 7,the lateral limitation of the virtual image IM (previous step f) iscarried out in such a way that the straight lines 13 and 14 cut thehorizon line 10 at points 11 and 12 which correspond, on a heading scaleof this virtual image IM, to the limit values of the heading scaledisplayed on the “ND” screen. For example, in numerous cases, theselimit values are equal to ±45° on either side of the current heading ofthe aircraft A, i.e. an angular discrepancy of 90° on the heading scalebetween said points 11 and 12.

[0090] More generally, according to the invention, the values of theangles θ1 and θ2 are chosen in such a way that the angular discrepancyon the heading scale between said points 11 and 12 lies in an intervalsubstantially equal to [40°; 140°]. Preferably, this angular discrepancyis chosen substantially equal to 90°. In a preferred embodiment, thevalues θ1 and θ2 are chosen substantially equal (the point O is thensubstantially at the center of the image IM).

[0091] In a preferred embodiment of the invention, the image IMconstructed in the aforesaid step e) comprises at least the followingelements, as is represented in FIGS. 9 and 10:

[0092] a symbol 20 representing the aircraft A, situated at the point 19of FIG. 8 and indicating its location;

[0093] a representation 21 illustrating the terrain;

[0094] a vertical reference stroke 22, preferably solid, between saidsymbol 20 of the aircraft A and its vertical projection onto saidterrain 21; and

[0095] a plot 23, preferably solid, representing the future trajectoryof the aircraft A.

[0096] The display screen 7 represented in FIGS. 9 and 10 is partiallycut away to facilitate the writing of the references.

[0097] The symbol 20 is fixed in the image IM in 3D and gives the pilotsa permanent and immediate reference when glancing at the display screen7. The terrain 21 shifts, it moves under the symbol 20, thus scrollingthe relief around the mock-up of the aircraft A. In order to fosterstraightforward comprehension of the image IM, the symbol 20 isrepresentative of the actual attitudes of the aircraft A in roll, pitchand yaw. This information is qualitatively reported on this symbol 20which tilts according to the three axes.

[0098] Additionally, the construction of the representation 21illustrating the terrain is effected on the basis of an onboard databaseforming part of said information sources 2, and constructed for exampleon the “WGS84” (GPS compatible) terrestrial benchmark. In a preferredembodiment, this representation 21 is constructed around elementarycubes 24 of variable dimensions representing a portion of terrain, asillustrated in FIG. 11, the upper ends 25 of said elementary cubes 24being connected together by a surface 26 which forms said representation21.

[0099] The accuracies required of this representation 21 depend on thezones overflown. Around airports, during critical phases of flight(initial climb and final approach in particular), the resolution must berefined so as to obtain an optimal terrain mesh consisting, for example,of squares (end surfaces 25) of 15″×15″. During cruising flight, widersquares of 3′×3′ are sufficient. A constant resolution is also possibleso as to display a fine accuracy, extended over the entire relief andwith no difference. These values are defined consistently with theresolutions of existing databases, which are carried on board theaircraft A. To comply with the safety objectives of the device 1, thedigital relief constructed must encompass the entire actual relief witha specified level of confidence; the elementary cubes 24 must thereforecompletely cover the terrain to be displayed.

[0100] Thus, the representation 21 illustrating the terrain is arealistic and intuitive representation, which fosters immediateawareness of the actual geography. This terrain-smoothing operationensures optimal safety and allows faithful modeling of the outsiderelief.

[0101] In a preferred embodiment, the image IM constructed in theaforesaid step e) also comprises a grid associated with therepresentation 21 of the terrain. This grid corresponds to the verticalprojection of the edges of the upper ends 25 of the elementary cubes 24onto the surface 26 forming said representation 21. Such a mode ofrepresentation allows proper qualitative comprehension of the concept ofdistance. It also allows better visual perception of the perspectiveeffect.

[0102] Naturally, it is also possible, as a variant, to represent onlysaid elementary cubes 24 without carrying out any smoothing.

[0103] It will be noted that said representation 21 illustrating theterrain can include obstacles created by man (towers, bridges, etc).These obstacles may be integrated into the aforesaid onboard database orinto a specific database.

[0104] In a preferred embodiment, the terrain altitude taken intoaccount in the representation 21 is multiplied by a coefficient k whosevalue lies in an interval substantially equal to [1.5; 2.5]. Preferably,the coefficient k is substantially equal to 2. The application of such amultiplier coefficient makes it possible to amplify the altitudes andtherefore to improve the perception of reliefs.

[0105] In a preferred embodiment, the points situated in front of theaircraft A at a distance greater than a predetermined distance L3 arenot represented on the virtual image IM constructed in the plane ofprojection PP. They may be replaced in this image by a uniformcoloration for the entire set of said points. This uniform colorationmay for example be gray or white, so as to be perceived visually asmist. Preferably, the value L3 is chosen equal to the maximum distanceused on a plan view, represented on a “ND” type navigation screen, thatis to say the zone situated in front of the aircraft A and which isdisplayed on this “ND” screen, L3 being limited moreover to a value of150 kilometers (around 80 Nm) beyond which the perspective no longerallows details to be distinguished. To facilitate the understanding ofthe perspective, it may be useful, on the one hand, to display on thescreen 7, for example in a rectangle 27 represented in FIG. 9, the valueof the maximum distance chosen and to modify the size of the symbol 20which becomes larger and larger as said maximum distance decreases.

[0106] Additionally, said vertical stroke 22 represented between thesymbol 20 of the aircraft A and its vertical projection onto the terrain21 comprises a scale 29 consisting of horizontal marks 29A placed onthis vertical stroke 22 so as to indicate predetermined distances underthe aircraft A. For example, these marks 29A are spaced apart by adistance corresponding to a value of 500 feet (around 150 meters) andthe number of marks 29A is limited to five, so as not to overload thedisplay.

[0107] In a particular embodiment, said vertical reference stroke 22also comprises a safety altitude indication, not represented.

[0108] Additionally, a symbol 28 is represented at the intersection ofsaid vertical stroke 22 and of the terrain 21 so as to allowvisualisation of the vertical projection of the aircraft A on theterrain 21. This symbol 28 may for example be gray and resemble a“shadow” of the aircraft A. The pilot thus clearly marks a lateraldeviation, in particular in case of simultaneous projection of theflight plan.

[0109] It will be noted moreover that the representation of the plot 23of the future trajectory is necessary so as to allow the crew toanticipate dangerous situations. The presentation of this trajectoryhelps to improve the situational awareness of the pilot. Futuretrajectory is the name given to the prediction of the trajectoryactually followed by the aircraft A. Naturally, the determination of thefuture trajectory 23 depends on the mode of piloting used on theaircraft A.

[0110] In manual mode, the trajectory 23 represented is a straight linecorresponding to the instantaneous trajectory of the aircraft A. Thelength represented of this future trajectory 23 corresponds to a flightduration over a short period (since it is not possible to predict thefuture actions of the pilot) lying for example between 30 seconds and 3minutes. In the particular case where the aircraft A performs acontinuous turn, the future trajectory. 23 can correspond to anextrapolation of this continuous turn for a predetermined duration.

[0111] In selected mode (that is to say when the automatic pilot of theaircraft A is controlled by the pilot, through a selection of heading,of altitude and/or of speed), the length represented of this futuretrajectory 23, calculated as a function of the parameters provided tothe automatic pilot, corresponds to a flight duration over a medium-termperiod, lying for example between 3 minutes and 10 minutes.

[0112] In managed mode (that is to say when the automatic pilot iscontrolled by a flight management computer of “FMS” type: “FlightManagement System”), the length represented of this future trajectory 23corresponds to a flight duration over a medium-term period of forexample between 3 minutes and 10 minutes. In this case, the trajectoryrepresented is therefore that calculated by said “FMS” computer.

[0113] In will be noted that a mixture of the managed and selected modesis possible, depending on whether the lateral guidance or the verticalguidance of the aircraft A is considered. For-example, a selected modeis possible for vertical guidance and a managed mode for lateralguidance.

[0114] Additionally, it should be noted that the representations of thefuture trajectory and of its vertical projection onto the terrain may beeffected in such a way as to be representative of the mode of piloting(manual, selected, managed or mixture of selected and managed), inparticular depending on the color, the thickness or the type (continuousor dashed) of stroke used. For example, it is conceivable to use acontinuous yellow stroke for the future trajectory in manual mode, acontinuous blue stroke for its vertical projection onto the terrain, acontinuous green stroke for the future trajectory in selected mode, adashed green stroke for the future trajectory in managed mode, etc.

[0115] Additionally, the image IM constructed in the aforesaid step e)furthermore comprises, as represented in FIG. 9:

[0116] plot 30 representing the vertical projection onto said terrain 21of the future trajectory 23 of the aircraft A;

[0117] a plurality of vertical strokes 31 between points 32 situated onsaid plot 23 representing the future trajectory of the aircraft A andthe corresponding vertical projections 33 of these points 32 onto saidterrain 21. Preferably, said points 32 correspond to the scheduledposition of the aircraft A at various intervals of time or of distance,for example each minute during the next 5 minutes. Furthermore, at leastone of said vertical strokes 31 comprises a safety altitude indication.

[0118] In an embodiment not represented, a safety altitude isrepresented, on a vertical stroke 31 in the form of a specificcoloration, for example magenta, of that part of said stroke which issituated under this safety altitude. In the case where the altitude ofthe aircraft A (respectively of a point 32 situated on the futuretrajectory 23) is less than this safety altitude, this vertical stroke31 is extended upward to an altitude corresponding to this safetyaltitude. The symbol 20 of the aircraft A (respectively a point 32 ofthe future trajectory 23) then lies under the upper part of therepresentation of the safety altitude. This constitutes a simple andimmediate visual mark of a potentially dangerous situation. Thisinformation may also be represented in digital form.

[0119] Additionally, the image IM also comprises a heading scale 34represented above the horizon line 10.

[0120] As well as the heading scale 34 proper, supplementary symbols maybe disposed on the image IM, on or in immediate proximity to saidheading scale 34. A first symbol 35, consisting for example of avertical yellow mark, can indicate the current heading (projection ofthe longitudinal axis AL of the aircraft A onto the heading scale 34). Asecond symbol 36, consisting for example of a green diamond and situatedat the point 17 of FIG. 8, can indicate the current course DR of theaircraft A. A third symbol 37, consisting for example of a cyan coloredtriangle, can indicate the heading or the course chosen by the pilot (inthe selected mode).

[0121] Additionally, the image IM constructed in step e) furthermorecomprises a flight plan 38. The flight plan 38 is displayed on theentire image IM, at the pilot's request. The flight plan 38 correspondsto the ideal trajectory programmed for example by the pilot into theflight management computer. Said flight plan 38 is artificially splitinto various subparts. In a preferred embodiment, the flight plan 38comprises:

[0122] a trajectory 39 in space, represented for example by dashes andaccompanied by a symbol 39A to specify the position of the aircraft Awith respect to this trajectory 39 in space;

[0123] a ground projection (not represented) of this trajectory 39; and

[0124] vertical references (waypoints along the course, displayed in theform of vertical strokes 40 surmounted, for example, by a green or whitediamond).

[0125] Additionally, the image IM constructed in step e) furthermorecomprises complementary information which is for example displayed on astrip 41 envisaged on the display screen 7 above the 3D representation.This complementary information may in particular correspond to thereport of information customarily displayed on a “ND” screen, such asthe wind (direction and force), the speed of the aircraft, the nextwaypoint, etc.

[0126] In a preferred embodiment represented in FIG. 10, the terrain 21is colored as a function of the altitude margin (or discrepancy) betweenthe current altitude of the aircraft A and the altitude of said terrain21.

[0127] Thus, the terrain 21 is represented with a neutral color 43, whenthe value of its altitude is less than a first predetermined value A1 inrelation to the current altitude of the aircraft A. It is representedwith a first alarm color 44 when the value of its altitude lies betweensaid first value A1 and a second predetermined value A2, in relation tothe altitude of the aircraft A, and it is represented with a secondalarm color 45 when the value of its altitude is greater than saidsecond value A2. By way of nonlimiting example, the following preferredvalues may be indicated: A1 is equal to −500 feet [i.e. 500 feet (oraround 150 meters) below the current altitude of the aircraft A] and A2is equal to +2000 feet [i.e. 2000 feet (around 600 meters) above thecurrent altitude of the aircraft A]. Furthermore, by way ofillustration, said neutral color 43 corresponds to green, said firstalarm color 44 corresponds to yellow and said second alarm color 45corresponds to red.

[0128] Advantageously, when the aircraft. A performs a rapid descent[for example with a negative vertical speed of absolute value greaterthan 1000 feet per minute (around 300 meters per minute)], in order tobetter anticipate the altitude of this aircraft A when it overflys therelief, its current altitude mentioned in the process indicatedhereinabove is replaced with a calculated altitude corresponding to thescheduled altitude of the aircraft A (depending on its descentconditions) after a predetermined duration with respect to the currentinstant, for example substantially equal to 30 seconds.

[0129] Advantageously, the distance between the future trajectory 23 andthe terrain 21 is calculated and analysed so as to detect a risk ofcollision of the aircraft A with said terrain 21, by taking into accounta safety margin. If a zone of potential conflict exists, an alarm issignaled. For example, said zone of potential conflict 46 is colored inan alerting manner (color 48). The display of this zone may also flashand its frequency of flashing may be all the higher the closer the zoneof conflict is to the aircraft A.

[0130] In a preferred embodiment of the invention, the colors 43, 44, 45and 48 chosen for the representation of the terrain 21 are homogeneouswith those used by a standard terrain avoidance system on board theaircraft A.

[0131] Preferably, a (virtual) protection envelope is set in placearound the aircraft A and its future trajectory 23. This protectionenvelope makes it possible to detect any intrusion or approach of theterrain with a certain margin around the position of the aircraft A andof its future trajectory 23. This margin consists of a preset fixedmargin and of a margin taking account of the uncertainty of theinstruments, of the automatic facilities and of the terrain relateddatabase. The aircraft A is thus guaranteed to be in the envelope in theminutes to come, and to be so with a certain probability. The verticaland lateral dimensions of the envelope agreeing with the safetyobjectives of the function follow from this probability and from thechoice of preset safety margins. The protection envelope may, also berefined as a function of the flight phase, so as to avoid untimelyalarms and as a function of the accuracies of positioning of theaircraft A. Any zone entering this envelope is colored in an alertingmanner and flashing may be associated with it.

[0132] Additionally, when a threatening zone 46 is detected, an alarmlabel 47, presenting the time before impact, is displayed, as isrepresented in FIG. 10 (even when this conflict zone is situated outsidethe region visible on the screen 7). This countdown informationtherefore supplements the coloration of the threatening terrain.

[0133] Preferably, the detection of a risk of collision with the terrainis disabled in the phase of final approach with a view to landing so asnot to give rise to untimely alarms.

[0134] In a particular embodiment of the invention, as well as thedetection of a risk of collision of the future trajectory 23 with theterrain, one also carries out the detection of a risk of intersection ofthe trajectory 39 corresponding to the flight plan 38 of the aircraft A,with said terrain.

[0135] The device 1 in accordance with the invention, which makes itpossible to aid pilots to instantaneously ascertain the position of theaircraft A in its environment, at the present instant and in the minutesto come, therefore affords a valuable aid to the awareness of thesituation of the aircraft in relation to the terrain and considerablyincreases flight comfort and safety. Specifically, said device 1 makesit possible to present the pilots with intuitive and instinctiveinformation requiring no mental effort in order to be processed. Theinformation support used offers a synthetic and immediate picture. The3D. representation produced improves the pilot's overall situationalawareness as regards:

[0136] the outside environment;

[0137] the future trajectory 23 of the aircraft A with respect to theenvironment (terrain 21) and to the scheduled flight plan 38; and

[0138] possibly neighboring traffic and/or meteorological phenomena.

1. A process for constructing a synthetic image (IM) of the environmentof an aircraft (A) and presenting it to at least one pilot of saidaircraft (A), wherein: a) a first straight line (D2) passing through thelocation of the aircraft (A) and forming a first angle of lateralseparation α and a first angle of vertical separation β with the course(DR) of the aircraft (A) is determined; b) a first point (V) isdetermined, said point being situated on said first straight line (D2)to the rear of the aircraft (A) at a distance such that the verticalprojection (V1) of this first point (V) onto the horizontal planepassing through the location of the aircraft (A), is situated at apredetermined distance L1 from said location of the aircraft (A); c) aline of aim (LV) passing through said first point (V) and forming asecond angle of lateral separation va and a second angle of verticalseparation vb with a second straight line (D3) passing through saidfirst point (V) and parallel to said course (DR) of the aircraft (A) isdetermined; d) a plane of projection (PP) which is orthogonal to saidline of aim (LV) is defined; e) an image (IM) is constructed of at leasta part of the environment at least in front of the aircraft (A), withthe aid of a conical projection onto said plane of projection (PP) whiletaking account of said first point (V) as reference point of theprojection; f) said image (IM) is delimited laterally by two verticalstraight lines (8, 9) respectively cutting the horizon line (10) of theimage (IM) at second and third points (11, 12) which are such that, onthe one hand, the angle (θ1) between the line of aim (LV) and a thirdstraight line (13) passing through said first and second points (V, 11)corresponds to a predetermined angle and, on the other hand, the angle(θ2) between the line of aim (LV) and a fourth straight line (14)passing through said first and third points (V, 12) corresponds to apredetermined angle; g) the scale of the image (IM) thus delimited isadapted so as to match the straight line segment (15) which is formed bysaid second and third points (11, 12) and which defines the width of theimage (IM), to the width of a display screen (7) on which one wishes topresent said image (IM), and this image (IM) is delimited vertically asa function of the height of said display screen (7); and h) the image(IM) thus constructed representing a synthetic image is presented onsaid display screen (7).
 2. The process as claimed in claim 1, whereinsaid first angle of lateral separation α lies between 6° and 15°.
 3. Theprocess as claimed in claim 1, wherein said first angle of verticalseparation β lies between 3° and 10°.
 4. The process as claimed in claim1, wherein said predetermined distance L1 lies between 3 and 20kilometers.
 5. The process as claimed in claim 1, wherein said secondangle of lateral separation va is less than or equal to said first angleof lateral separation α.
 6. The process as claimed in claim 1, whereinsaid second angle of vertical separation vb is less than or equal tosaid first angle of vertical separation β.
 7. The process as claimed inclaim 1, wherein said display screen (7) is furnished with a headingscale (34) and said angles (θ1, θ2) between, on the one hand, the lineof aim (LV) and, on the other hand, said third and fourth straight lines(13, 14) are such that the angular discrepancy on the heading scale (34)between said second and third points (11, 12) lies between 40° and 140°.8. The process as claimed in claim 1, wherein in step g), the image (IM)is delimited vertically in such a way that the horizon line (10) of saidimage (IM) is situated in the upper third of said display screen (7). 9.The process as claimed in claim 1, wherein in step e), only an image ofthe environment which is situated up to a predetermined distance infront of the aircraft (A) is constructed.
 10. The process as claimed inclaim 1, wherein the image (IM) constructed in step e) comprises atleast the following elements: a first symbol (20) representing theaircraft (A) and indicating its location; a representation (21)illustrating the terrain; a vertical reference stroke (22) between saidsymbol (20) of the aircraft (A) and its vertical projection (28) on saidterrain (21); and a first plot (23) representing the future trajectoryof the aircraft (A).
 11. The process as claimed in claim 10, whereinsaid first symbol (20) representing the aircraft (A) is representativeof the attitudes of the aircraft (A) in roll, pitch and yaw.
 12. Theprocess as claimed in claim 10, wherein the image (IM) constructed instep e) furthermore comprises a second plot (30) representing thevertical projection onto said terrain (21) of the future trajectory (23)of the aircraft (A).
 13. The process as claimed in claim 10, wherein theimage (IM) constructed in step e) furthermore comprises a plurality ofvertical strokes (31) between points (32) situated on said first plot(23) representing the future trajectory of the aircraft (A) and thecorresponding vertical projections (33) of these points (32) onto saidterrain (21).
 14. The process as claimed in claim 13, wherein at leastone of said vertical strokes (31) comprises a safety altitudeindication.
 15. The process as claimed in claim 10, wherein the image(IM) constructed in step e) furthermore comprises a second symbol (28)situated at the intersection of said vertical reference stroke (22) andsaid representation (21) illustrating the terrain.
 16. The process asclaimed in claim 10, wherein said vertical reference stroke (22)comprises a scale (29).
 17. The process as claimed in claim 10, whereinsaid vertical reference stroke (22) comprises a safety altitudeindication.
 18. The process as claimed in claim 10, wherein the image(IM) constructed in step e) furthermore comprises a heading scale (34)represented above the horizon line (10).
 19. The process as claimed inclaim 10, wherein the image (IM) constructed in step e) furthermorecomprises a flight plan (38).
 20. The process as claimed in claim 10,wherein the image (IM) constructed in step e) furthermore comprisessupplementary information (41, 27).
 21. The process as claimed in claim10, wherein said representation (21) illustrating the terrain is coloredas a function of the discrepancy between the altitude of the aircraft(A) and the altitude of said terrain (21).
 22. The process as claimed inclaim 10, wherein the image (IM) constructed in step e) furthermorecomprises a grid which is associated with the representation (21) of theterrain and which corresponds to the vertical projection of the edges ofthe upper ends (25) of elementary cubes (24) onto a surface (26) formingsaid representation (21).
 23. The process as claimed in claim 10,wherein any risk of collision of the aircraft (A) with the terrain (21)is detected by calculating the distance between the future trajectory(23) of the aircraft (A) and said terrain (21), and a first alarmindication (45, 47) is presented on said image (IM) when such a risk ofcollision is detected.
 24. The process as claimed in claim 10, whereinany risk of intersection of a flight plan of the aircraft (A) with theterrain (21) is detected by calculating the distance between atrajectory (39) corresponding to this flight plan (38) of the aircraft(A) and said terrain (21), and a second alarm indication is presented onsaid image (IM) when such a risk of intersection is detected.
 25. Theprocess as claimed in claim 10, wherein a rotation of the line of aim(LV) by a predetermined angle about the aircraft (A) is carried out. 26.A device for constructing a synthetic image of the environment of anaircraft (A) and presenting it to at least one pilot of said aircraft(A), said device (1) comprising: information sources (2) comprisinginformation relating to the aircraft (A) and to its environment;information processing means (3) able to construct a synthetic image(IM) of the environment of the aircraft (A) on the basis of informationemanating from said information sources (2); and display means (5) ableto present, on at least one part of a display screen (7), said syntheticimage (IM), wherein said information processing means (3) are formed insuch a way as to implement the process specified under claim 1.